This invention relates, in general, to connectors for joining two tubular members together in axial relationship and, in particular, to a new and improved stab and latch tieback connector of the ratcheting type for use in joining tieback casing to a subsea well system to tieback the subsea well system to a drilling or production platform.
In offshore drilling and production, it is often necessary to connect and disconnect the lower end of a string of joined pipe sections, sometimes referred to as "marine risers" or "strings" of "casing" or "tieback conductors" which connect (tieback) a subsea well system to a floating or stationary platform sometimes referred to as a "rig."
The use of tieback conductors between the drilling or production platform and the subsea well and the need to connect and disconnect the subsea well system at the ocean floor (mudline) and the use of a tieback connector for this purpose is well known.
Present stab and latch tieback connectors, sometimes called "stab tools", connect the riser string by stabbing into the mudline casing hanger of the subsea well system and ratcheting across the internal threads of the casing hanger until the tool is secured within the casing hanger. The present stab tools of this type utilize a split ring having wicker type threads on its outer surface which perform the aforementioned ratcheting action and the ring expands and contracts as it ratchets until fully engaged with the threads of the casing hanger. The reverse taper on the mating faces of the wicker type thread helps eliminate a tendency for the wicker thread to be forced out of contact with the threads of the casing hanger by thread loading caused by tensioning of the riser string, i.e., pulling up on the string at the platform. However, even with such a reverse taper on the threads, disengagement under load is possible, and particularly if standard square shoulder threads are used in the casing hanger.